Manufacturers of caulking materials often package the materials in disposable cartridges. A cartridge typically is a wound fiberboard tube with an apertured metallic ring crimped to one end. A generally conical plastic member is carried by the ring to provide a closure and, when a portion near the tip is severed a desired amount, to provide a dispensing nozzle when the cartridge is used. The tube is substantially filled with caulking or other mastic material and a piston is inserted in the end portion of the tube opposite the ring.
Operator actuated caulking guns for dispensing caulk from cartridges have received wide acceptance. Such guns typically have a forward, apertured, slotted, tube restraining end. The nozzle is inserted through the aperture and the ring abuts the forward restraining end of the caulking gun. A plunger is provided to act against the caulking cartridge piston. The plunger is typically mounted on an elongated rod which is advanced through ratcheting action to apply dispensing pressure to the cartridge piston.
Typically such a caulking gun will include a handle which depends from the gun near the end remote from the restraining end, and a pivotal lever mounted in the handle. Actuation of the lever drives the rod forward through any one of a number of forms of ratcheting mechanisms to in turn drive the plunger against the piston.
A number of proposals have been made for utilizing pressurized gas for dispensing caulk. The objective of such proposals is to provide more uniform dispensing especially for professional tradesmen. They also seek to reduce operator fatigue and the occurrence of such problems as hand cramps when caulk dispensing operations are continued over a substantial period of time. While the proposals have had such objectives all have had material drawbacks with resultant limitations on their use.
A number of proposals have been made for pneumatically actuated dispensing guns. Most such proposals have relied on a connected supply of pressurized air which results in limitations as to locations where such guns can be used. In addition the connected air lines can interfere with use of such pneumatic dispensers and provide a drag on the movement of such a dispenser.
There has been at least one proposal for a pneumatically actuated caulking dispenser which did not require a connected air line. Rather, the device included a plenum chamber which was to be charged with a supply of pressurized air used to drive the piston. The piston in turn was housed in a cylinder and connected to a projecting rod which drove a plunger. In short, the plenum chamber and the piston and the cylinder were relatively heavy and bulky substitutes for the ratcheting mechanism in the conventional hand-actuated caulking gun.
A mechanical structure was provided to normally prevent piston motion and selectively enable it. One disadvantage to such an arrangement is obviously once the mechanics experience some wear, constant pressure application against the piston is apt to cause unintended discharge of caulking material. Another disadvantage of this proposal is that pressure available to dispense caulk is obviously continuously decreasing as the volume occupied by the air increases during dispensing operations. Unless there is a very large and structurally strong structure defining the plenum the performance of such a pneumatically actuated gun could obviously continuously decline as caulking operations are performed.
A further problem with the proposed pneumatically charged gun is so-called "after ooze", a problem present with most prior art caulking dispensers. As the caulk is pressurized to effect the dispensing operation, air or other gases entrained in the mastic material are compressed. When dispensing pressure stops these entrained gases expand to their original volume causing the mastic material to continue to flow out the nozzle, the so-called after ooze. The proposal for a pneumatically charged gun would deal with the after ooze problem by providing an operator actuated mechanism to drive the piston rearwardly at the conclusion of a caulk-applying operation to permit the caulk to expand rearwardly rather than cause continued flow out the nozzle. Thus, while the proposal would eliminate the need for operator-applied force to expel caulk it would create such a need to prevent after ooze, and that force would have to be applied against substantial air pressure.
Others have proposed the use of carbon dioxide cartridges or other liquefied gas containers connected to and carried by the material dispensing mechanisms. These devices are unduly complex and heavy and exhibited several problems. When caulk is to be dispensed the valve is opened to allow carbon dioxide gases to escape from the cartridge and be supplied to a piston actuating chamber in the gun. At the conclusion of the dispensing operation, to deal with the after ooze problem, such a chamber was to be vented. This not only is wasteful of the pressurized gas but exacerbates a second problem. The second problem is that such a device is attitude sensitive. That is, if the gun is positioned in certain attitudes when the valve is open to effect a dispensing operation, liquid carbon dioxide will flow through the valve into the chamber being charged. Once that has happened caulk flow cannot be stopped until either (1) enough CO.sub.2 has been vented to the atmosphere to cause all of the liquefied CO.sub.2 in the chamber to become gaseous and the pressure reduced to the point where it is low enough the caulk will not be expelled or (2) enough caulk has been expelled to permit complete gasification of the CO.sub.2. Unfortunately, the latter may not occur until the entire contents of the caulking tube has been dispensed.
Another problem with fluid actuated devices has also been discovered. The problem is that the seal
between the wall of the tube and the tube's piston may not prevent liquefied gas from flowing inside the tube, especially where the tube is plastic. As a result, fluid is able to get in front of the piston and work its way down toward the nozzle so that when caulk is expelled from the nozzle, bubbles of liquefied gas are also expelled. The popping of the bubbles dispensed from the device results in "sputtering", or the random distribution of small particles of caulk.
A further problem with CO.sub.2 cartridge actuated devices is that as the liquefied CO.sub.2 expands and passes through the control valve in gaseous form it is absorbing heat. This can result in the valve being frozen open, frosting of valve surfaces and other undesirable effects.
Some relatively expensive materials such as silicone gasket forming materials have been sold in disposable pressurized carriers. While such disposable pressurized dispensers have been used, their use has been limited to relatively expensive materials for low volume application and would be uneconomic if used for such applications as dispensing the caulking compounds used by house painters.
There has been at least one proposal for a CO.sub.2 actuated mastic material dispenser of a CO.sub.2 actuated device in which it was proposed to control the flow of material at the outlet. The device was unduly complex and heavy, was difficult to clean, and would only accept the cartridges of the type which take a screw-on nozzle rather than the far more readily available type in which a disposable conical tip is provided that is cut to form the nozzle.